Keller F. Suberkropp Professor, (past)

This study is designed to examine the role of dissolved nutrients (N and P) in regulating the growth and activity of leaf-decomposing stream fungi. Most quantitative studies of stream fungal communities have occurred in streams with high nutrient concentrations. Consequently, little is known concerning fungal activities in streams with low nutrient concentrations even though much of our current understanding of stream ecosystem function has come from studies of such systems. Rates of fungal growth and sporulation, concentrations of fungal biomass and fungal production in both hardwater and softwater streams with very low nutrient concentrations will be determined and compared with similar data from streams containing higher nutrient concentrations. Recently, a method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol has been described. This method has been adapted for use with stream fungal communities and will be used on decomposing leaf litter in the study streams. These data, together with determination of ergosterol contents as a measure of fungal biomass will allow estimation of fungal production during leaf degradation and in streams over an annual cycle. Both types of production estimates will be used in the comparative studies mentioned above. The effects of N and P will be measured directly in field experiments in which water flowing through streamside artificial channels will be amended with N, P or both nutrients and the response of fungal communities determined. Organic matter budgets for fungal isolates from nutrient poor and nutrient rich streams growing on leaf litter in environmental simulating laboratory studies will be constructed to determine if fungi exhibit different strategies of resource allocation in response to varying nutrient concentrations. This project will provide the first research effort concentrating on the role of nutrient limitation of fungal community structure and biomass in streams. The PI will be using a novel technique to measure fungal growth rates and community structure.Fungi have been demonstrated to play key roles in mediating energy flow in the detritus-based food chains in streams. Until recently, however, there have been no methods available that would allow determination of instantaneous growth rates of fungi in any environment. Consequently, quantitative data concerning fungal production or flow of energy through the fungal community are not available. A method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol was recently described. The proposed studies are designed to adapt and evaluate this method for use on the leaf-decomposing fungal communities in streams. Laboratory studies will establish optimum conditions for the incorporation of acetate into ergosterol and determine factors for converting incorporation rates into growth rates of individual fungal species. Laboratory studies of individual species growing on leaf material will be used to compare estimates of growth rates and production determined by the 14C-acetate method with production estimates determined independently from changes in fungal biomass, respiration and conidium production. The method will then be used to estimate growth rates and production of fungal communities during the decomposition of leaves in two streams that differ in water chemistry. These results will be compared with other measures of activity including total microbial respiration, total microbial biomass and sporulation rates of stream fungi. These studies will contribute to the assessment of a new method that has the potential to make a significant impact on our understanding of fungal activities in the environment and should contribute needed information concerning the productivity of fungi in streams. My research interests focus on the ecology of stream fungi and their role in plant litter decomposition including interactions with invertebrate detritivores. This study is designed to examine the role of dissolved nutrients (N and P) in regulating the growth and activity of leaf-decomposing stream fungi. Most quantitative studies of stream fungal communities have occurred in streams with high nutrient concentrations. Consequently, little is known concerning fungal activities in streams with low nutrient concentrations even though much of our current understanding of stream ecosystem function has come from studies of such systems. Rates of fungal growth and sporulation, concentrations of fungal biomass and fungal production in both hardwater and softwater streams with very low nutrient concentrations will be determined and compared with similar data from streams containing higher nutrient concentrations. Recently, a method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol has been described. This method has been adapted for use with stream fungal communities and will be used on decomposing leaf litter in the study streams. These data, together with determination of ergosterol contents as a measure of fungal biomass will allow estimation of fungal production during leaf degradation and in streams over an annual cycle. Both types of production estimates will be used in the comparative studies mentioned above. The effects of N and P will be measured directly in field experiments in which water flowing through streamside artificial channels will be amended with N, P or both nutrients and the response of fungal communities determined. Organic matter budgets for fungal isolates from nutrient poor and nutrient rich streams growing on leaf litter in environmental simulating laboratory studies will be constructed to determine if fungi exhibit different strategies of resource allocation in response to varying nutrient concentrations. This project will provide the first research effort concentrating on the role of nutrient limitation of fungal community structure and biomass in streams. The PI will be using a novel technique to measure fungal growth rates and community structure.Fungi have been demonstrated to play key roles in mediating energy flow in the detritus-based food chains in streams. Until recently, however, there have been no methods available that would allow determination of instantaneous growth rates of fungi in any environment. Consequently, quantitative data concerning fungal production or flow of energy through the fungal community are not available. A method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol was recently described. The proposed studies are designed to adapt and evaluate this method for use on the leaf-decomposing fungal communities in streams. Laboratory studies will establish optimum conditions for the incorporation of acetate into ergosterol and determine factors for converting incorporation rates into growth rates of individual fungal species. Laboratory studies of individual species growing on leaf material will be used to compare estimates of growth rates and production determined by the 14C-acetate method with production estimates determined independently from changes in fungal biomass, respiration and conidium production. The method will then be used to estimate growth rates and production of fungal communities during the decomposition of leaves in two streams that differ in water chemistry. These results will be compared with other measures of activity including total microbial respiration, total microbial biomass and sporulation rates of stream fungi. These studies will contribute to the assessment of a new method that has the potential to make a significant impact on our understanding of fungal activities in the environment and should contribute needed information concerning the productivity of fungi in streams.

Ecology, Environmental Biology, Water Resources